1. Technical Field
The present disclosure relates to the treatment of glaucoma. More particularly, the present disclosure relates to medical devices and methods for creating a drainage pathway to divert aqueous humor out of the anterior chamber of the eye such that pressure within the eye is reduced.
2. State of the Art
Glaucoma, a progressive ocular disease that manifests itself through elevated intraocular pressure (“IOP”), is one of the leading causes of preventable blindness. When the pressure in the eye remains sufficiently high for a long enough period of time, blindness or total vision loss may occur. If properly treated, the pressure within a glaucomic eye may be reduced and the possibility of blindness may be averted.
The anatomy of the eye is described with reference to FIG. 1. The eye 10 includes an iris 12, which is a colored circular muscle that controls the size of the pupil 21, which is an opening located in the center of the iris 12. By adjusting the size of the pupil 21, the amount of light that is allowed to enter the eye can be adjusted in response to light conditions. A cornea 14, which is a transparent external surface, covers the pupil 21 and the iris 12. The area of the eye above the lens 22 and under the cornea 14 comprises the anterior chamber 16.
The sclera 28, which is the white of the eye, is a tough outer membrane that covers the entire eye 10, except for the portion of the eye 10 that is covered by the cornea 14. The area or junction where the cornea 14 merges into the sclera 28 is known as the limbus 25. A portion of the sclera 28 is covered by a thin tissue called the Tenon's membrane (also called the Tenons Capsule) 34, which envelopes the bulb of the eye 10 from the optic nerve (not shown) to the ciliary body 18 of the eye 10. The conjunctiva 36 lines the inside of the eyelids (not shown) and overlies the Tenon's membrane 34 and the sclera 28.
The trabecular meshwork 24 is a wedge-shaped structure composed of collagen beams arranged in a three-dimensional sieve-like structure. The beams are lined with a monolayer of cells called trabecular cells. The spaces between the collagen beams are filled with an extracellular substance that is produced by the trabecular cells. These cells also produce enzymes that degrade the extracellular material. The trabecular meshwork 24 and the Schlemm's canal 26 are located at or near the angle 30, which is the angle formed at the vertex of the iris 12 and the cornea 14. The outer wall of the trabecular meshwork 24 coincides with the inner wall of Schlemm's canal 26.
Schlemm's canal 26 is a tube-like structure that runs around the circumference of the cornea 14. In human adults, Schlemm's canal 26 is believed to be divided by septa into a series of autonomous, dead-end canals. Aqueous humor travels through the spaces between the trabecular beams of the trabecular meshwork 24, into Schlemm's canal 26, and through a series of collecting channels that drain from Schlemm's canal 26 and into the episcleral venous system (not shown).
The anterior chamber 16, which is the space between the iris 12 and the cornea 14, contains a clear fluid called aqueous humor, which is essential for the proper functioning of the eye. Aqueous humor is formed by the ciliary body 18 which is adjacent to the posterior chamber 20 of the eye 10. The aqueous humor, which is made at a fairly constant rate, passes around the lens 22, through the pupil 21 in the iris 12 and into the anterior chamber 16. The aqueous humor naturally drains out of the anterior chamber 14 primarily through the trabecular meshwork 24 and Schlemm's canal 26.
In a normal patient, aqueous humor production is equal to aqueous humor outflow and intraocular pressure remains fairly constant, typically in the 8 to 18 mmHg range. If the production of aqueous humor is not balanced by its proper drainage, the aqueous humor will build up to a high level of intraocular pressure (or IOP) and cause glaucoma.
Various devices have been designed to treat glaucoma by alleviating the IOP within the eye. Examples of such devices may be found in U.S. Pat. Nos. 7,431,709; 7,594,899; 7,837,644; and U.S. Pat. Pub. No. 2013/0184631, the contents of each of which are incorporated herein in their entireties.
One such device for treating glaucoma will now be described with reference to FIGS. 1 and 2. A drainage implantation device 100 includes a tube 102 having a lumen 104 extending lengthwise through the tube 102, and a protrusion or fin 106 extending radially outward from the exterior of the tube 102 as shown in FIG. 2. The fin 106 is configured to prevent the tube 102 from migrating and to prevent the leakage of aqueous humor from around the tube 102 (i.e., peri-annular leakage) once the device 100 is implanted in a patient's eye as shown in FIG. 2. The tube 102 has an inlet end 108 disposed opposite an exit end 110. During implantation, the inlet end 108 is positioned within the anterior chamber 16 of the eye, and the exit end 110 is positioned within a space (or pouch) 114 that is formed primarily between Tenon's membrane 34 and the sclera 28 by physical dissection of the conjunctiva 36 and Tenon's membrane from the sclera 28 with scissors as evident from FIG. 2. The tube 102 extends through a needle tract 116 through the sclera 28 leading to the anterior chamber 16. The needle tract 116 may be formed from a 25 gauge (G) needle (which is approximately 0.020″ or 0.51 mm in diameter). The inlet end 108 of the tuber 102 can have a diameter that is approximately 0.013″ or 0.33 mm, which is smaller than the diameter of the needle, which facilitates maneuvering of the inlet end 108 through the needle tract 116 into the anterior chamber 16. The fin 106 has a diameter than is larger than the diameter of the needle and thus larger than the needle tract 116. In this configuration, the fin 106 may be wedged into scleral tissue of the needle tract 116 and act as a stopper where the scleral tissue seals against the exterior surface of the fin 106 and thus prevent peri-annular leakage. Preventing such uncontrolled leakage of aqueous humor out of the anterior chamber 16 is desirable because hypotony (very low IOP) may otherwise result, thereby damaging the eye.
The device 100 may be delivered to the implantation site via a hollow needle. To reduce the possibility of damaging the eye from the insertion of the needle therethrough, it is desirable that the needle be as narrow as possible. However, since the device 100 is to translate through the needle, the needle must necessarily have a greater diameter than that of the device 100. Often, such needles have incorporated slots, extending along the length of the needle to accommodate the fin 106 of the tube 102 of the device 100 as the tube 102 translates through a lumen extending lengthwise through the needle.
Unfortunately, the use of a slotted, hollow needle may present a few noteworthy challenges and difficulties. For example, a slotted needle may not penetrate the sclera 28 of the eye 10 as easily as a needle that does not have such a slot. In particular, the missing section of the slotted needle may impede the insertion of the needle through the sclera 28. Therefore, the force necessary to penetrate the sclera 28 may be greater when using a slotted needle as compared to a needle that does not have such a slot. Since it is desirable that the forces required to insert the needle through the sclera be as small as possible such that the possibility of trauma to the eye is kept to a minimum, the use of a slotted needle poses a challenge. Another challenge may be translating the implant, e.g., device 100, to the implantation site as it may be difficult to push a relatively soft tube through a hollow needle because the soft tube may expand sufficiently to become jammed in the hollow space of the needle.